The five kingdoms classification system of life consists of the Monera, which includes the bacteria and archaebacteria; Protista, which includes protozoa, slime molds and algae; Fungi; Plantae; and Animalia. The five kingdom classification system is outdated, as the bacteria and archaebacteria are now recognized as being different enough to be in separate kingdoms. These two groups do share the lack of a nucleus, an organelle which all other kingdoms possess.
Monera and Protista both consist of mostly single-celled organisms, although they are quite different from one another. The most defining difference is that, not only do organisms in Monera lack any nucleus, they lack any of the membrane-bound organelles which are typical of Protista. In addition, some protists, as members of Protista are called, are truly multicellular, with division of labor between cells. These are all algaes, such as kelp. In addition, some slime molds form relatively huge, macroscopic single cells containing many nuclei. Protists are very diverse, including both photosynthesizing species and consumers, and some which do both.
Fungi are mostly multicellular organisms with cell walls that acquire nutrients by absorption, often from decaying organic material. Plants are universally photosynthetic organisms, also with cell walls. Animals lack cell walls and are by far the most mobile of the multicellular species.,